Over the past two decades, researchers have come to think of skeletal muscle as being more than just machinery. Rather, it’s an endocrine organ that manufactures and releases chemical messengers into your bloodstream.
This reframe has important implications for how we think about exercise.
Meet the Myokines
The chemical messengers produced by muscle tissue are called myokines, and there are hundreds of them.
When a muscle contracts, it releases these substances into circulation, where they act on the brain, liver, fat tissue, bone, blood vessels, and immune system.
In other words, your muscles communicate with the rest of your body. Constantly. And whether or not you’re exercising your muscles regularly has a lot to do with what they’re saying.
Following are a few of the better-studied examples:
- IL-6 is released in significant quantities during exercise. This myokine has a somewhat confusing reputation because chronically elevated IL-6 from other sources is considered inflammatory. However, exercise-induced IL-6 behaves differently, mobilizing fuel and anti-inflammatory responses downstream.
- Irisin influences fat tissue and has been studied for its potential role in converting white fat into more metabolically active brown fat.
- BDNF (brain-derived neurotrophic factor) supports the growth and survival of neurons. Muscle contraction contributes to circulating BDNF, which helps to explain the well-documented relationship between physical activity and brain health.
- Osteocalcin-stimulating signals help to drive bone remodeling, which is at least in part why weight-bearing exercise strengthens skeletal bone.
What This Changes
Here’s why this shift in thinking is important:
If muscle were just machinery, then losing some of it as you age would largely be an inconvenience (in the form of reduced strength).
But if muscle is an endocrine organ, then losing muscle mass means losing an entire signaling system.
This helps to answer questions that have long puzzled clinicians:
- Why do measures of muscle mass and strength track so closely with health outcomes that seem unrelated to strength?
- Why is grip strength a good predictor of cardiovascular events?
- Why does a loss in muscle mass correlate with a loss in cognitive function?
- Why is sarcopenia (i.e. age-related muscle loss) associated with higher mortality rates, even after accounting for obvious mechanical consequences?
The myokine story offers a plausible explanation. Muscle isn’t just holding you up. It’s providing system-wide regulation.
Here’s the Catch
Myokines are released when muscle contracts.
Simply having muscle isn’t enough. A muscle sitting idle isn’t signaling in any significant way. This is why a sedentary lifestyle is correlated with health risks that aren’t fully offset by one single workout (i.e. because your muscles are essentially silent for most of the remainder of the day).
It also means this benefit is renewable. Every time you use your muscles, they’re communicating and regulating.
What This Means in Practical Terms
The implications to all of this are refreshingly simple:
- Strength train. Two to four sessions per week. This preserves the tissue doing the signaling.
- Break up time spent sitting. Short movement breaks throughout the day keep the conversation going.
- Eat sufficient protein. Most adults over 40 under-consume protein, and muscle can’t be maintained without this raw material.
- Use your glutes and your legs. Your lower body has the biggest muscles and therefore has the greatest signaling capacity.
Where Hormones Come In
None of this works well without the right hormonal environment:
- Testosterone drives muscle protein synthesis (the process by which training stimulus actually becomes new tissue) in both women and men.
- Growth hormone supports tissue repair between workouts.
- Thyroid hormones set the metabolic pace at which all of this happens.
- Estrogen contributes to muscle maintenance (in both women and men).
When these hormones decline with age, muscle becomes progressively harder to build. It also becomes easier to lose. People often experience this as putting in the same amount of effort, but with less to show for it. This is because effort isn’t the problem. It’s the signals (in the form of hormones) that have weakened.
In short, your hormones support your muscles. And your muscles support the rest of your body (in more ways than one).
At Renew Youth, we help men and women to preserve muscle mass through physician-supervised hormone therapy and comprehensive healthy aging strategies. To learn more, call us at (800) 859-7511 or use our easy contact form to schedule your complimentary 30-minute consultation.